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采用水文统计法,以北洛河流域丘陵沟壑区、高塬沟壑区、阶地平原区以及林区等不同地貌类型和覆被区水文测站资料为基础,分析其近50年来流域径流变化趋势、程度以及极端降雨事件下的稳定性,对比辨析区域尺度流域径流演变特征和控制因素。结果显示,总体上北洛河流域年径流量呈显著减少趋势,年均变率为-0.19mm/a。林区流域径流比较稳定,而非林区流域,无论哪种地貌类型,均呈显著减少趋势,变幅为-0.11~-0.66mm/a。丘陵沟壑区年径流量发生跃变时间在1999年左右,高塬沟壑区和阶地平原区变化时间则在1994年。在水文序列的3个阶段,即1979年前、1979年后水土流失治理效应期以及1999年后的退耕还林时期,丰水流量(5%)不受地貌类型差异和森林覆被与否的影响,各流域均呈持续减小趋势。而枯水流量(95%),受水土流失综合治理影响,各流域首先表现出一致地增加趋势,然后受退耕植被恢复类型和程度影响,在不同地貌类型间有差异。以草灌恢复为主的丘陵沟壑区流域,枯水流量持续增加,以林灌恢复为主的高塬沟壑区和阶地平原区反而呈减少趋势。平水流量(50%)在各流域间反应均变化较小。多重分形临界指数分析认为,总体上阶地平原区和林区流域径流稳定性最好,其次为高塬沟壑区,丘陵沟壑区稳定性最差。区域水土流失综合治理和植被恢复,对各流域1%~5%和5%~50%频域下的降雨-产流调控作用均比较有效,而对≤1%极端降雨事件的作用有限。结果表明,森林覆盖与否及植被恢复类型等生态因素,而不是地貌类型,控制着区域尺度径流演变过程和程度。
The hydrological statistic method was used to analyze the runoff change trend in the past 50 years on the basis of the data of hydrological stations with different landform types and covering areas such as the hilly and gully areas in the Beiluohe River basin, the gully area in the highland, terraced plain areas and the forest areas, Extent and stability under extreme rainfall events, and to analyze the characteristics and controlling factors of runoff evolution in regional scale watersheds. The results showed that on the whole, the annual runoff of the Beiluohe River Basin decreased significantly with an average annual rate of -0.19mm / a. The runoff in the forest area is relatively stable, whereas in the non-forest area, no matter what kind of landform, it shows a significant decreasing trend with amplitude of -0.11 ~ -0.66mm / a. The annual runoff in the hilly and gully areas of the hilly and gully areas took place around the year of 1999, while that of the highland and gully areas changed in 1994. In the three stages of hydrological sequence, that is, before and after 1979, the era of soil and water loss control after 1979 and the period of returning farmland to forest after 1999, the abundant water flow (5%) is not affected by the difference of landform type and forest cover or not Impact, all the watershed showed a decreasing trend. The low flow rate (95%) is affected by the comprehensive management of soil and water loss. The watersheds first show a consistent trend of increase and then are affected by the types and degrees of restoration of vegetation and the difference in different types of landforms. In the gully area where grassland irrigated and reclaimed, the flow of low water continued to increase, whereas the highland and gully areas dominated by forest and irrigation showed a decreasing trend instead. Flat water flow (50%) showed a small change in response across the catchments. Multi-fractal critical index analysis shows that, on the whole, the runoff stability is the best in the terrace plains area and the forest area, followed by the highland and gully area, and the worst in the hilly and gully areas. Integrated control of regional soil erosion and vegetation restoration are more effective at controlling rainfall and runoff in the frequency ranges of 1% ~ 5% and 5% ~ 50% in all watersheds, but have limited effects on extreme rainfall events of ≤1%. The results show that ecological factors such as forest cover or vegetation restoration types, rather than landform types, control the evolution and extent of regional scale runoff.